Planning brine/water heat pump, who has experience with it?

Hello dear forum members,

I graduated a few years ago in building energy technology in Bremerhaven and I am also a gas and water installer. Now, I have only worked in the industry for a short time and unfortunately I simply lack experience in this field. Of course, I have theoretically done all of this once, but by now that is almost no longer true.

My wife and I are planning to build a house this year and I have put together a rough idea of the system technology as a placeholder for a cost estimate. Now everything is becoming quite a bit more concrete and I am realizing that without advice from more experienced colleagues, I cannot fully understand my plans until the end. I know that people usually use the informal "du" in forums; whoever does not like that, please feel free to be addressed formally and do not hold it against me. That’s a little about me and my background.

Now to the matter. So far, we are planning to build the following house:

-KfW40plus

-150 m² living space

-underfloor heating everywhere

-about 20W/m², so 3 kW heating load

-3-4 person household, so an additional approx. 0.8 - 1.2 kW come on top (how this value comes about I have not fully understood yet, but it is always recommended everywhere to add 0.2 - 0.3 kW per person)

-I read everywhere about lockout times with special heat pump tariffs. If such exists and is realistic, I would also like to factor that in. For example, heating load (or the total power?) x 1.3 or something in that direction

Well, if I now add all this up for the worst case, I am already close to 5.5 kW. I would like a device from Weishaupt or Vaillant. Weishaupt is out because the hot water storage tank there, I think over 300 l, is much too large for me. So the Vaillant device with a 185 l hot water storage tank remains.

The choice: flexoCOMPACT exclusive VWF 57/4 with about 5.4 kW

Now I have also heard of modulating (and also more expensive) devices from other manufacturers and I wonder whether it makes sense for me to continue pursuing my Vaillant placeholder or if I should look around further and consider other products.

I do not want to have a buffer tank but I am trying to think about every case. How does the system usually behave, for example, in the transitional phases when the underfloor heating just barely switches on and I have a quite low demand. The 3 kW are really only the worst case and you do not constantly reach that. I worry that this system could cycle a lot and just keep turning on and off. I also cannot estimate the hot water preparation with the heat pump at all.

My question at this point is, can you support me a bit with your experience and share your opinion on this matter? Am I heading toward a solid plan here or is it already a mess from the start? Is the heat pump sufficient with the connected underfloor heating or should I put a small buffer in between? (lockout times, cycling) Do you maybe have experience with the system itself? Can you perhaps also recommend other manufacturers, although I have planned the other technology so far also from Vaillant and can save myself complicated controls if I take the complete package. I am really grateful for every little thing.

Best regards Sebastian

For these specific questions, a forum that specializes in building services engineering and whose signal color is pink is more suitable.

For these specific questions, a forum that specializes in building services engineering and whose signal color is pink is more suitable

and additionally, take a look at the funding conditions of the BAFA. You can get a 5000€ subsidy there. But a master craftsman definitely has to sign off on it. Doing it all yourself down to the last detail could actually be uneconomical.

You should check whether a special heat pump tariff (with the mentioned blackout periods) even makes sense. Especially considering the low heating and hot water demand (probably under 2,000 kWh p.a.), it could be that the additional costs for the second meter (including ongoing costs) are higher than the savings per kWh over the year. If in your imagination photovoltaic systems are also involved somewhere, the rationale behind the two-meter strategy practically collapses immediately.

And we have a 200l hot water tank with 2 adults and 2 children... it works well, but with two adults/children taking longer showers one after the other, it’s not feasible. You should (especially with your wife!) discuss whether you are willing to do that, or you will have to wait about half an hour in between. Otherwise, feel free to take the 300l. But you can calculate that well... tank times desired temperature and flow rate per minute at 38°... you know what I mean.